3-52
3-103 The power that could be produced by a water wheel is to be determined.
Properties The density of water is taken to be 1000 m3/kg (Table A-3).
Analysis The power production is determined from
W
UVg ( z 2 z1 )
m g ( z 2 z1 )
§ 1 kJ/kg ·
(1000 kg/m 3 )(0.400/60 m 3 /s)(9.81 m/s 2 )(10 m)¨
¸
© 1000 m 2 /s 2 ¹
0.654 kW
3-104 The flow of air through a flow channel is considered. The diameter of the wind channel downstream
from the rotor and the power produced by the windmill are to be determined.
Analysis The specific volume of the air is
v
(0.287 kPa ˜ m 3 /kg ˜ K)(293 K)
100 kPa
RT
P
0.8409 m 3 /kg
The diameter of the wind channel downstream from
the rotor is
A1V1
A2V 2 
o(SD12 / 4)V1

o D 2
D1
V1
V2
(7 m)
(SD 22 / 4)V 2
10 m/s
9 m/s
7.38 m
The mass flow rate through the wind mill is
m
A1V1
S (7 m) 2 (10 m/s)
v
4(0.8409 m 3 /kg)
457.7 kg/s
The power produced is then
W
m
V12 V 22
2
(457.7 kg/s)
(10 m/s) 2 (9 m/s) 2 § 1 kJ/kg ·
¨
¸
2
© 1000 m 2 /s 2 ¹
4.35 kW
PROPRIETARY MATERIAL. © 2008 The McGraw-Hill Companies, Inc. Limited distribution permitted only to teachers and
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